The popularity of "micro" flow irrigation systems (e.g., rated from approximately 1.0 gph to 60.0 gph) for garden and related agricultural uses, has dictated the need for pressure modulating flow control valves that will communicate a near constant flow rate to a water distributing device, such as a sprayer or drip type emitter. Systems of this type include a main water line in the form of a plastic tube and a series of suitably spaced smaller plastic tubes or branch lines interconnected between the main water line and each water distributing device. In addition to the problem of not providing a substantially constant flow rate of water to the distributing device, many conventional systems are prone to clogging.
Various pressure-compensating flow control valves have been proposed for solving the above, briefly described problems in the field of irrigation. For example, applicant's U.S. Pat. No. Re 29,022 discloses various embodiments of a self-flushing and pressure compensating irrigation valve that will function to maintain a predetermined near constant flow rate of water at the outlet thereof in response to fluctuations of main line water pressure. Although valves of this type work quite well for many irrigation applications, there is a need for a less complex valve hat can be manufactured economically and installed or replaced more expeditiously.
Further, pressure modulating valves of the latter type are oftentimes designed to have flexible lips, composed of a highly flexible elastomeric material, that are entirely surrounded by water at the inlet to the valve. Flexing and deformation of the lips during operation render it difficult, at times, to closely calibrate and closely control the desired near constant flow rate of the valve.